Factory automation systems often include one or more Programmable Logic Controllers (PLCs) coupled to other devices, such as remote I/O devices, over one or more communication networks. In a factory or other industrial setting, such networks may include dozens or hundreds of sensors that constantly monitor such things as temperatures, fluid levels, or robotic arm positions. The sensors may be coupled to one or more remote I/O devices that report back to the PLC many times per second. The PLC may include rules for acting on the changing conditions, such as issuing commands to other devices over the network to perform various operations in the system.
As one example, the Ethernet/Industrial Protocol (EtherNet/IP) network standard allows industrial devices to communicate over an Ethernet-like network. When the network is first initialized, devices communicate with each other regarding the frequency with which each device will send out updates (e.g., once every 10 milliseconds) and a time-out value (usually specified as a multiplicative factor related to the update frequency) specifying the time after which a particular device will be deemed to have failed if no update is received (e.g., 40 milliseconds). For example, upon initialization, a PLC may transmit messages to remote I/O devices instructing each device to report updates according to a specified schedule (sometimes referred to as “scanning rates” or “requested packet interval” or RPI for short), and providing device time-out values. Thereafter, when the system is operational, each remote I/O device may take measurements or perform other functions (e.g., setting a switch, turning on a motor, or controlling a valve) based on the instructed scanning rate and time-out value.
One difficulty that can arise in such networks is that there may be a need to change the scanning rates for one or more I/O devices once the system is operational. Unfortunately, changing the rates may require shutting down the system (stopping the PLC and/or rebooting various devices in the network) in order to load new values into the devices. This is because in EtherNet/IP-based systems, the connection to the affected device must be dropped and then re-initiated using new parameters. Such an operation may lead to sequencing problems between the PLC and the affected device and/or possible loss of data, which may be unacceptable. Shutting down an industrial system, particularly for a large factory or other industrial plant, may be costly. It would therefore be desirable to permit parameters, such as scanning rates and time-out values, to be modified without requiring the stopping and restarting various devices.